By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester
This Naturalist Note is dedicated to Phil Hamilton who passed away on June 12. Phil devoted more than 24,000 volunteer hours helping make Tryon Creek State Natural Area the wonderful place it is today. He played many leadership and resource roles, but is perhaps best known as the ‘King of the Ivy Pullers.’ He not only pulled a lot of ivy himself, but led hundreds of groups of ivy pullers out into the park. Every time I went out with him, he told me something brand new about the forest that I did not know before. He was a great role model, and helped many people get started on the track of volunteering at Tryon Creek. I, and I’m sure many others, will remember this dedicated, knowledgeable and hard-working man forever. Thank you Phil!
If there was a vote on the most despised plant at Tryon Creek State Natural Area (TCSNA), ivy would win hands down. This aggressive, invasive plant outcompetes and displaces many native plants. In an area near the Red Fox Trail where the ivy completely covered the forest floor, I removed and measured the ivy in a three-foot by three-foot plot. In that plot there were 285.8 linear feet of the ivy vine. (Yes, it was really thick, in multiple layers!) If (and thankfully, it doesn’t) this density of ivy covered all of TCSNA there would be enough ivy to wrap around the earth at the equator more than 6 times!
Ivy’s habit of climbing up tree trunks makes it difficult to ignore. Not surprisingly, ivy has many special features that make it so successful.
Ivy: The ingenious climber
Ivy needs sunlight to grow. How does a plant get close to the sun? Most trees, like our Douglas-fir (Pseudotsuga menziesii) develop a thick trunk that lifts their leaves up toward the sun. Building the thick stem takes a lot of resources. A study in western Washington showed that for 47-year-old Douglas-fir, 87% of the above ground biomass was in the trunk of the tree. The major purpose of the tree trunk is to get the needles up into the sunlight where they can photosynthesize. The ivy developed the habit of just climbing the tree trunks that were already there. It saved itself all the energy required to develop a self-supporting stem.
I pulled down an ivy vine that was growing up the side of a tree. The diameter of the ivy’s stem at ground level was 3/4 of an inch. Twenty-one feet up the tree, it was not much smaller, as you can see below:
Since ivy doesn’t need a thick stem to hold itself erect, it uses its energy to grow taller.
In contrast, a western redcedar (Thuja plicata) only 10 feet tall growing along Old Main Trail had a basal diameter of 1.59 inches. The redcedar needs this thick stem to hold itself up, while the ivy doesn’t.
Not that ivy vines don’t grow large, especially when two or more vines merge together.
Ivy only had to develop a method of holding onto the tree. Voilà! The aerial rootlet, which adheres to the tree’s bark:
Using these aerial rootlets, the ivy manages to climb up the trunk of trees into the light without having to expend the energy to develop a big, supportive stem.
Creating a Home for Others
While we rarely envision ivy as a benevolent plant, other organisms may have a different view. As you can see in the photo below, sometimes the mass of ivy stems creeping up a tree is part of a community complex most frequently involving moss or licorice fern (Polypodium glycyrrhiza). While removing ivy from a tree near the Red Fox Trail, I collected the sample (in cross section) shown below. It is a combination of primarily ivy and licorice fern, with a hint of moss.
The mass of roots, stems and miscellaneous dirt measured about 7 cm (~2-1/2 inches) thick.
How much water might this hold? I cut a 2-1/2” by 3-1/4” sample from the tree. I soaked it overnight in water. I weighed the wet sample and then let it air dry completely and weighed it again. I calculated that a square foot of this material would hold slightly more than 2-1/4 quarts of water. This is a mixed blessing. While some of this is a nice reservoir of water for the licorice fern growing in this mass, it is also a significant weight burden for the tree.
To find out how much water might be stored in the mass of ivy roots and licorice fern, I did some calculations. I measured the diameter of the trunk of a large fallen alder tree near the Middle Creek Trail at 10 foot intervals, up to 63 feet above ground, where it started branching out. Based on this data, I calculated the surface area of the tree trunk. If the entire surface of this tree trunk were covered like the sample above, the ivy/moss/licorice fern could potentially contain up to 1,520 lbs. of water. That’s three-quarters of a ton of water. Yikes!
Ivy: It’s Tough
Every species of plant contains nutritious chemicals like sugar, cellulose and dozens of others. This naturally attracts other species that don’t have the ability to capture solar energy to sustain themselves. One of the keys to a plant’s survival is to protect itself from these organisms, which range from molds and insects, all the way to humans. In the picture below, you can see the surviving remnants of leaves on one of TCSNA’s common shrubs.
To find out how effective ivy is in protecting itself, I conducted a survey in the fall of 2016. I examined the leaves of three species of plants, and counted the number of leaves (or leaflets) that were damaged. To minimize the possible effects of humans, I examined sites more than 10 feet from a trail. (Confession: I don’t actually know what caused the damage; it might have been insects, diseases, a hailstorm or whatever.) For each species, I examined leaves in two different places (for example, near Red Fox Trail and near Old Main Trail), to get an “average” value.
The results are presented below:
Number of Total leaves Percent of
Species damaged leaves examined leaves damaged
Red Alder 181 199 90.0%
Oregon grape 375 559 67.1%
Ivy 93 279 33.3%
Ivy has less leaf damage, whatever the cause, than either the red alder or the Oregon grape. Good for the ivy!
Ivy is a Persistent Grower
Every plant has a growing season, and for ivy, it’s long. To determine how long into the fall/winter this plant might grow, I measured the growth of an individual ivy stem along the Red Fox Trail. The data shows that ivy continues growing quite late in the year.
In contrast to the ivy, on September 28, one of the Indian plum (Oemleria cerasiformis) plants I was monitoring in that area was completely bare of leaves, while the other Indian plum in that area had dropped about 98% of its leaves.
Ivy’s Secret Strategy
One of ivy’s secret strategies is that virtually every place along the stem where there is a leaf, there is the potential to grow roots. That is seen in the photo below:
Should the stem of this ivy plant be broken, no sweat! Every part of the stem has its own root system and can stay alive. This is in contrast to most woody plants which only produce roots at a single point in the plant.
English Ivy really isn’t that bad (a tidbit for geeks!)
It turns out that much, if not most, of the ivy that we have at the park really isn’t English ivy (Hedera helix); it’s Irish ivy (Hedera hibernica). Not that the other plants care!
The key reliable morphological feature that discriminates between the two species are the miniature hairs that grow in clusters on the plant. The Irish ivy hairs are in small clusters lying flat on the plant’s surface, while English ivy hairs are in larger clusters and stand erect. The microphotographs below of plants collected at TCSNA shows the difference.
To further complicate things, hybrids of English and Irish ivy have been discovered and…. Okay, I’ll quit now!
The Ivies: Green Success Stories
The ivies in the genus Hedera are very successful plants. They can grow tall without having to use their own stem to support themselves. When hacked into pieces, many of the pieces are able to stay alive and become a whole new plant. They also appear more resistant to disease and predation than many of TCSNA’s other plants. They have a longer growing season than many of our native plants. All of this spells success for the plant, and lots of work for our ivy pullers who are trying to encourage the growth of native plants by reducing the resource competition from the ivy!
By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester
Western trillium (Trillium ovatum) flowers are a major attraction at Tryon Creek State Natural Area (TCSNA). I’ve already written three Naturalist Notes about this plant. In the process I’ve accumulated a host of materials that didn’t fit too well with any of those previous notes; the time has come to share them.
How big do trilliums grow?
From May 4 through May 6, 2016, I conducted a survey of trilliums that were growing more than 10 feet from any trail. The areas I surveyed were near the Equestrian and North Horse Loop Trails in the northern part of the park, Center, Big Fir and Old Main Trails in the central part of the park, and Iron Mountain Trail in the southern part of the park. For each triple-leafed trillium I encountered I measured the distance from the ground to the attachment point of the triple “leaves.” I also noted whether or not each plant was flowering. The results are shown below.
Ten inches is about the height where the plants shift from non-flowering to flowering, although a couple of very short plants flowered, and a few fairly tall ones didn’t.
What happens to the trillium’s flowers and seed pods?
Ideally, the flowers are pollinated, the seed pods (or capsules) mature, then open and release their seeds into the forest. Of course there are other possibilities. Deer, it has been reported, sometimes eat the flowers. The contents of the maturing seed pod are very nutritious, and researchers have reported that both deer and mice sometimes eat the seed pods.
To assess this, I conducted surveys in two different years. The first survey was conducted between June 23 and 28, 2015. Two groups of trilliums were surveyed. “Trailside trilliums” were those growing within 10 feet of the trail. “Mid-forest trilliums” were those growing more than 10 feet from the trail. It should be noted that at this time the seed pods are well along the path to maturity. The plants were placed in three categories: a) capsule intact, b) pedicel only, meaning the plant had flowered, but the flower/seed capsule was missing, and c) did not flower, as indicated by having no pedicel or capsule. Illustrations of each class are below:
The results are shown below:
A statistical analysis (Note to nerds: I used the Chi-squared test.) clearly shows that a significantly higher percentage of the trailside plants flowered compared to plants growing more than 10 feet from the trail. The cause of this difference cannot be determined by this study. The other statistically significant difference between these two groups is that a higher percentage of the “mid-forest” trilliums only had a pedicel (“flower stalk”), which means that either the flower or the seedpod was removed. Animals likely ate these seed pods or flowers. Perhaps the deer are more comfortable eating in the middle of the forest than trailside.
In 2016 I undertook a second trillium survey, this one was conducted May 4 through May 6, at a time when the last of the trillium petals had just recently fallen off the plants. This time, however, the “trailside plants” I tallied were within 3 feet of the trail. The “off-trail plants” were growing more than 10 feet from a trail. At this time the seed capsules were small and immature. The results are shown below:
Once again, the percentage of plants flowering was statistically significantly higher in the trailside plants compared to plants growing “off-trail”. A slightly smaller percentage of the flowers/seed-capsules had been eaten than in the previous study, probably because there was a shorter period of time for the animals to eat them, or perhaps, being smaller, they were of less interest to the animals. The one thing that clearly stood out in the data is that the percentage of reproductive structures missing was significantly higher along Old Main Trail than along the other trails. (Geek note: Statistically, there is less than a 1 in 10,000 probability that the higher percentage of missing capsules observed along Old Main was due to chance.) The fact that Old Main is one of the most heavily traveled trails makes it tempting to speculate that people were picking these flowers, as shown in the picture below, but this study cannot prove that.
An alternative explanation for the empty pedicels is that the flower was defective and the defective bloom was aborted. I recently saw a single dysfunctional bloom in the forest. It appears that the plant started to produce a functional flower, but something bad happened along the way, as in the example below, where you have what appears to be an attempt at a flower, but no actual petals.
Does it really take 7 years for a trillium to recover after the flower is picked?
Many people believe that if you pick a trillium it will be 7 years before the plant flowers again. I unexpectedly got a chance to test that theory when someone picked 6 trillium flowers on a plot of trilliums I had been studying for 5 years. I concluded these had been picked, because the remaining stems did not exhibit the type of cut associated with animal browsing. One of the stems from which the flower had been picked is shown below:
Although very unhappy, I decided to capitalize on the tragedy. (“When life hands you a lemon, make lemonade!”) I carefully documented the exact location of the trilliums. Based on the location of the six flowers, it appeared that all of them were twin stems, arising from a total of only three rhizomes (rhizomes are like a flower bulb).
In April 2017, one year after the tragedy, I surveyed the site again. I went to the site and measured the location of the trilliums. Based on their location, 2 flowering stems were within ½” of the location of the flowering stems that were decapitated last year. Thus I concluded that only 2 out of the 3 effected rhizomes produced flowering stalks again this year. However, whereas last year they were twin-stalked, this year they only had one stalk each. At the location of the third picked trillium, there was nothing. Scientists have determined that some years a trillium will occasionally just take a rest, and not produce an above ground stem. So that is what this one did, OR it died. I don’t know which. Either way, for at least two of the plants, the “7 year” myth is debunked.
Does anything eat trilliums?
Deer are commonly reported to eat trilliums. But it turns out that isn’t the whole story. This spring I ran across one of our slimy forest friends deeply engrossed with a trillium. Note that this is not our native banana slug (Ariolimax columbianus) but appears to be one of the non-native species.
You’ll notice that considerable chunks of the trillium petals are also missing, and these may only have been the prelude to the slug’s full scale attack on the heart of the trillium flower.
What pollinates trilliums?
Most of the plants we hear about are pollinated by bees, like our Pacific waterleaf (Hydrophyllum tenuipes), or by the wind, like Douglas-fir (Pseudotsuga menziesii). Trilliums are a little different. A study of Trillium ovatum in southern Oregon determined that pollinators included several species of beetles, honey bees, bumble bees, crab spiders and geometrid moths1. Since the trillium doesn’t produce nectar, at least some of these creatures are here to eat the pollen, and they spread the pollen as an unintended side effect.
The forest is endlessly fascinating, when a person just stops to observe. Looking back on my old trillium photos, I now see lots of the “little brown bugs” deep down in the bloom. How could I have missed that so often? When you’re out in our forest, stop for a minute and look around. I think you’ll be amazed, as I was, at how many interesting things are out there.
1Jules, Erik S. and Beverly J. Rathcke. 1999. Mechanisms of Reduced Trillium Recruitment along Edges of Old-Growth Forest Fragments. Conservation Biology 13:784-793.
By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester
This year January brought us an unusually wet, heavy snow. In my Lake Oswego backyard, it amounted to just over 7-1/2 inches of the white stuff. The snow at Tryon Creek State Natural Area (TCSNA) was roughly similar. As with so many other unusual events, it was a great opportunity to learn more about our forest.
The wet, heavy snow brought many changes. Some that we humans, entranced with the visual wonder that is our forest, tend to regard as tragic. But Nature may have a different view. Let’s take a look at some of the things that happened.
Look out below!
All kinds of trees fell down. As shown in the photo below, the top snapped off from this red alder (Alnus rubra) growing near Red Fox Bridge. You can see the top lying on the ground. For the alder, this is a horrific setback, if not death.
However, the plants growing on the ground under this alder may have a different perspective. I stood right over the alder trunk lying on the ground, pointed my camera upwards and took this picture of a significant hole in the canopy.
Do you suppose the plants growing on the ground are looking up and thinking, “Oh what a tragedy. Now we’re going to be growing in full, life-giving sunlight, and we won’t have competition from the alder.” No matter what kind of tragedy it was for the tree that fell down, many of the neighboring plants will be celebrating because of the extra sunlight they will be receiving.
And if the existing plants already on the ground aren’t able to jump in and take advantage of the newly sunny spot, rest assured that some new plants will. The photo below shows numerous red alder seeds (two are marked with red arrows) on the Middle Creek Trail the very same day I photographed the broken alder. Finding these tiny seeds in the forested area would be very difficult, but have no doubt, they are there!
Death Cleanses the Forest
Perhaps you mourn the loss of so many good trees. In at least some cases, your tears are wasted. A storm like the one we had can be viewed in part as Nature cleaning up the forest. For example, as part of a human cleanup effort, I spent some time cutting through the trunk of a western redcedar (Thuja plicata) that was lying across the Cedar Trail so the trail would become passable (see photo below).
It was sad because it was a young tree, with potential to become one of the esteemed elders of the forest. Or so I thought. As I dragged some of the branches off the trail, I noticed the top of this tree (pictured below).
The top four to five feet of this tree had already been dead for some time. So the real story was that this tree was already having problems of one kind or another, and the storm just ended its struggle. Since it already had a dead top, its long term potential was not as great as I originally thought.
In another case, a very tall (about 115 foot) Douglas-fir (Pseudotsuga menziesii) fell down across the Old Main Trail. This is another tree that I cleared off the trail (Note: The clean-up work I did after the storm proved very educational. You might want to give it a try!) The top was forked due to some damage many years ago, as indicated in the picture below.
But this is another example of a tree that was already in trouble. The smaller branch on the right side of the picture shown above had been damaged many years before this year’s storm, as you can see below.
I sawed off the top 12” of this stub, and inserted a pencil into the soft rotten area in the center of the stem. The results are shown below.
I could easily stick the pencil a couple inches into the rotten wood. I cut 2 more feet off the end of this stub, and was still able to stick the pencil about ½” into the rotten center of the branch. Once the fungus gains this much of a foothold in a tree, it’s only a matter of time before it seriously weakens the tree.
So once again, the storm felled a tree that was already in trouble.
Dead Trees Can be Useful
And if you mourn for the dying trees, rest assured that not all of the forest inhabitants share your grief. Bark beetles lay eggs under the bark, and their larvae start burrowing through and eating the soft nutritious tissues that are right under the bark. Of the hundreds of species of bark beetles, at least some attack after the tree is dead. These beetles leave the kind of tracks like those you can see after the bark has been removed from this branch collected at TCSNA.
And of course, once insects get into a tree, can woodpeckers be far behind? The photo below shows a heavily “wood-peckered” long-dead tree along Old Main Trail.
And Some Weird Stuff…
The snow also brought at least one unique observational opportunity! Down near the creek in one area, I noticed that the snow had patches of yellow color. (No, it’s not THAT!) There were no animal tracks in this area, so I seriously doubt the yellow patches were from dogs or coyotes. According to reports on the internet, yellow snow in this context is frequently the result of pollen getting mixed in with the snow. Sadly, I got a picture, but never collected a snow sample for microscopic examination. The storm was roughly at the time that some hazel (Corylus spp.) would be shedding its pollen, but I have no proof that’s what it is.
Assuming this is pollen, I have no doubt that pollen is shed like this on the ground every year. However, it takes a snow covered forest floor before we will ever notice it.
Our Ever Changing Forest
Our forest is an ever changing ecosystem. If we could see this forest in 400 years, much of it would look unfamiliar. Most often the change is very slow, but a catastrophic event like a dramatic storm puts the changes in a time context we humans can relate to. Enjoy our forest today, because when you come back tomorrow, it will be different.